Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare destructiveHint=true, idempotentHint=false, and readOnlyHint=false, so the safety profile is covered. The description adds real value beyond that by disclosing the side-effect scope: messages and usage travel with the number, which the schema does not express. It still omits what happens to a prior customer's attribution and whether the operation can fail partway.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

A single compact sentence with no filler, and the primary action is front-loaded ahead of the unassign case. The leading 'Platforms:' qualifier is slightly cryptic and spends words without clear payoff.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a two-parameter mutation with full schema coverage, no output schema, and annotations that already flag destructiveness and non-idempotency, the description covers both operating modes. Only the edge-case behavior around reassignment of an already-assigned number is left unstated.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and both parameters are documented, including 'null to unassign'. The description only restates the null-unassign behavior already present in the schema and adds nothing about the E.164 format or ownership constraints, so the schema carries the load and baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: attribute a phone number, along with its messages and usage, to a customer, or clear the assignment. This is unambiguous about what the tool does. It does not name or distinguish itself from adjacent siblings such as bulk_update_numbers, link_number_to_registration, or update_customer, so it stops short of a 5.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implicitly tells the agent to use customer_id=null when unassigning, which covers one usage branch. However, it gives no guidance on when to prefer this tool over bulk_update_numbers, link_number_to_registration, or update_customer, and states no prerequisites such as ownership or permissions.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.